1. Field of the Invention
This invention relates to heat sealing machines, and more particularly, to a machine for heat sealing thermoplastic material bags or pouches.
2. Prior Art
Small manually actuated heat sealing machines specifically designed for use with plastics materials pouches have been previously proposed. Such devices are used in closing plastic material pouches after items have been placed in the pouch. A typical use is found in hospitals and other areas where sterile items must be stored. Pouches for such items are normally either formed of thermoplastic material, or of combinations of paper or other fiber material and thermoplastic material, and must be sealed at one edge after insertion of the item in the pouch.
Such sealing devices normally utilize opposed jaw members with one of the jaw members being heated and the other jaw member being provided with a resilient facing. After the pouch or other item to be sealed is placed between the jaws, a mechanism is provided which is operator actuatable to cause the jaws to seat for a period of time. The period of time can either be determined by the time that an activating switch, such as a foot switch, is depressed, or it can be determined by the mechanism which holds the jaws closed.
An example of the latter type is shown in U.S. Pat. No. 4,229,244, where a gear motor is used to rotate a configured cam face against a cam follower on one end of a lever arm to force the other end towards the fixed jaw. The movable jaw is attached to the other end and is thus forced into engagement with the fixed heated jaw. As the cam face is rotated, a reduced radius section is presented to the cam follower allowing the jaw to drop away from the fixed jaw. Thus, the cycle time is controlled by the revolution time of the cam face.
Other devices have used other mechanisms for moving the movable jaw, such as, for example, an eccentric attachment of a link affixed to the movable jaw, or in larger production type machines, pneumatic or hydraulic cylinders actuated against the movable jaw. Some devices have allowed a selection of seal shapes by changing jaw faces.
Such prior machines have deficiencies in that (among others) the cycle time can vary, the mechanism used to force the jaws closed is subject to many variables or is quite expensive and susceptible to damage and in rigid connection systems the closure pressure varies greatly with pouch thickness.
Additionally, prior devices normally had only one predetermined cycle time and one predetermined heat setting. Different types of plastics material and different types of pouches may require both different heats, different seal areas, and different jaw closed dwell times. It would be an advance in the art to provide an improved heat sealer which is capable of being used with both of the common types of sterile plastic packaging, i.e. all plastic and part plastic and part paper, which is economical to manufacture and is reliable, where the cycle time is more precisely controlled, and where thick pouches will not result in potential damage.